(1) Field of the Invention
The present invention relates to an improvement of the soldering technique adopted in the production of a honeycomb body assembled by soldering a metal foil or metal sheet. More particularly, the present invention relates to a method of effectively coating a solder on a portion to be bonded of a honeycomb body in the production of a plate-fin heat exchanger or a metal carrier for a catalyst for purging an exhaust gas from an automobile engine or the like.
(2) Description of the Related Art
A radiator or plate-fin heat exchanger is constructed by a honeycomb structure body (hereinafter referred to as "honeycomb body") formed by piling flat plates and corrugated plates in the form of layers and soldering the plates to one another. The supply of a solder to this honeycomb body is generally accomplished by alternatively piling flat plates and corrugated plates having both surfaces spray-coated with a powdery solder, or by inserting a solder foil between every two adjacent flat and corrugated plates and piling the plates.
A metal carrier for a catalyst for purging an exhaust gas is constructed by a honeycomb body formed by alternately winding or laminating flat metal foils (hereinafter referred to as "flat foils") and corrugated metal foils (hereinafter referred to as "corrugated foils"). As the method of soldering this honeycomb body, there is known a method in which a portion close to the end face of the honeycomb body (hereinafter referred to as "end face portion") is immersed in a binder liquid, a powdery solder is scattered in the interior of the honeycomb body from the end face of the end face portion, the solder is applied to the end face portion immersed in the binder liquid, and the soldering is carried out (see Japanese Unexamined Patent Publication No. 61-199574).
According to this conventional solder-supplying method, however, it is difficult to uniformly supply a necessary amount of a solder only to the portion to be bonded of the honeycomb body, i.e., the portion defined by the apex of the corrugated foil (plate) and the flat foil (plate), and the following problems arise.
(1) Since the solder is supplied also to a portion not to be bonded, the amount of solder used is increased. Moreover, since the total amount of the solder is increased, components of the solder are diffused into the metal foil and corrosion or contraction often occur.
Namely, if the end face portion of the honeycomb body is immersed in the binder liquid, as is taught in the above-mentioned patent publication, the binder adheres to a portion other than the contacting portions of the flat foil and corrugated foil, i.e., the surfaces of the flat foil and corrugated foil, and therefore, the solder also adheres to this portion and the above-mentioned problem arises.
(2) Where the solder is first supplied to at least one of the flat and corrugated plates, flat plates and corrugated plates are alternately piled in the form of layers, and are wound to form a honeycomb body, and subsequently the honeycomb body is soldered. Because, however, the solder is inserted between the flat and corrugated plates, the apparent thickness of the honeycomb body is increased, it is difficult to precisely estimate, before the soldering, the thickness after soldering, and to adjust the thickness accordingly.
(3) Where a cylindrical honeycomb body is prepared by supplying a solder to at least one of the flat and corrugated plates and piling and spirally winding these plates, a space formed after the melting of the solder at the soldering step cannot be eliminated, and therefore, the method in which the solder is inserted between the flat and corrugated plates cannot be adopted. For this reason, the solder must be supplied to the portion to be bonded after the corrugated and flat plates have been piled and spirally wound, and therefore, according to the conventional solder-supplying method, it is difficult to supply a necessary amount of the solder only to the vicinity of the portion to be bonded.
(4) As the means for supplying a solder precisely to the vicinity of a portion to be bonded, there can be mentioned the dispensing system in which a mixture of a gelatinous binder and a powdery solder is extruded little by little from a fine nozzle. According to this system, however, since the nozzle is manually operated, the operation efficiency is low when the mixture is supplied to many bonding points, as in case of bonding a honeycomb body, and it is often impossible to bring the nozzle close to the bonding points.